1. Field of the Invention
This invention relates to transformers, more specifically, to multi-layer ceramic transformers and methods.
2. Description of Related Art
Transformers of conventional construction incorporate windings and magnetically permeable areas referred to as cores. Windings generally consist of an insulated conductive wire and is usually wrapped around a magnetic core. The windings may also be wrapped around an insulated bobbin which is then placed around a magnetic core. It is common for transformers to incorporate several windings of different turns or wraps to comprise the primary windings and the secondary windings.
Conventional transformers have long incorporated separate magnetic core and winding areas making them restrictive in terms of placing the windings relative to the core. Generally, the windings are wound around the magnetic core, thus adding to the overall size and volume of the transformer. It is impractical, using current construction techniques, to physically pass the windings through the core region. To do this would be very costly and time consuming. Furthermore, most of the possible circuit paths passing through a magnetic core material would induce unwanted magnetic fields in addition to the magnetic fields produced by design. Therefore, wrapping the windings around a magnetic core region limits the options for reducing the size of a conventional transformer. Reducing the size of an isolation transformer is often difficult because the physical size and construction of an isolation transformer play a role in its electrical isolation properties.
In addition to physical size limitations, conventional transformers that are used in telecommunications applications must also conform to regulatory safety standards because to a great extent they are used for isolating user electronic equipment from a communications network, e.g. telephone network. Many regulatory agencies require that a transformer provide a certain voltage isolation barrier and meet certain clearance and creepage distance requirements within the transformer.
Clearance distance, defined as the shortest distance between two conductive parts measured through air, is of particular concern because air, albeit a good insulator, given a strong enough electrical field, will eventually ionize and breach the dielectric barrier.
Creepage distance, defined as the shortest distance between two conducting parts measured along the surface of the insulation, is also of particular importance, because given enough electrical potential between two points on an insulating surface, under suitable environmental conditions, and enough time, the surface of the insulation will eventually break down and lead to a breach in its isolation properties.
Conventional transformers are manufactured to meet distance and voltage isolation requirements by using insulating tapes, cross over tapes, varnish, epoxy, insulating wires and plastic bobbins. These are used in a variety of combinations to ensure that the transformers will withstand the required voltage breakdown limits and the specified distances.
In addition to physical size limitations and electrical insulating properties limitations, a conventional transformer is not easily manufactured in an automated fashion. Conventional wire wound transformers are difficult to manufacture in an automated fashion because of the need to solder winding leads to bobbin terminals. Additionally, wrapping the windings and keeping them away from each other during the manufacturing process is rather difficult and requires a lot of manual labor to assemble. Simple changes in regulatory requirements calling for higher voltage isolation would potentially require additional processing and result in an increase of the transformer's cost beyond what the market will bear.
To overcome the limitations of conventional transformers, a number of methods of manufacturing ceramic transformers have been disclosed. Most of these ceramic transformers do not adequately address electrical isolation requirements, such as the physical requirements needed to give adequate voltage breakdown protection.
Additionally, the conventional ceramic transformers that meet the safety requirements often do not provide adequate performance, such as a poor coupling between coils of a conventional ceramic transformer, etc.
Thus, there is a need in the art for an improved transformer and method, in particular, a low cost, small size, ceramic transformer that can be readily mass produced in an automated fashion and also meet regulatory safety requirements.